Over the last few years a series of ophthalmic devices of the aforementioned type have been developed, based upon a slit illumination of a section of the cornea and upon the recording of such an illuminated section through a suitable observation system. Most of such devices capture and record images of various sections of the eye, through rotation of the capturing devices around the optical axis of the eye and, through suitable processing, they obtain a three-dimensional reconstruction of the anterior chamber of the same eye.
One of the main problems that has been experienced when using this kind of devices is that the eyes of the patient, however cooperative and concentrated he may be on correctly fixing the fixation point provided by the device, cannot keep absolutely still. On the other hand the scanning of the eye requires a certain period of time in order to be completed. Therefore, what occurs is that during the rotating scanning, the ideal position for capturing the eye becomes misaligned with respect to the rotation axis of the capturing device. This misalignment, when positioning the single sections with respect to one another and therefore in the three-dimensional reconstruction phase of the anterior chamber, can lead to artefacts and considerable errors.
In order to solve this problem, different “a posteriori” correction methods have been proposed and implemented in devices that are currently on the market. An example of such a way to approach the problem is provided by the device described in EP1430829. Indeed, a specific functional solution forms the object of such a patent, that is, simultaneously recording sectional images and front images, the latter showing an image of the illuminated sectional portion of the cornea, so as to make it possible to assign a section captured at a time T to the area that is indeed illuminated, formed by the front image.
This second solution has the following drawbacks:                saving the image twice (from the front and from the side) means an extra functional workload of the examination and an increase in the computational costs;        compensation a posteriori, in any case, does not offer a completely satisfactory solution, since it is necessary for there to be a mathematical interpolation of the data when assigning them to their position again, and an interpolation is of course less reliable than a direct data measurement.        
Active correction solutions are also known. For example, U.S. Pat. No. 7,712,899 describes a solution with two perpendicular channels for simultaneously recording two sections of the eye and a third video observation channel, that is capable of detecting the possible misalignment of the eye and the consequent correction through the movement of a considerable part of the two recording systems of the sections.
A system of this kind however, in turn, is structurally and operatively complex, and therefore its practical application comes up against constructive problems, control difficulties and inaccuracy of the results.